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The Gut-Brain Connection

The trillions of bacteria in your gut shape more than just your waistline. They influence your mental health, stress response, and even mood and depression.

By Christine Yu

Trust your gut.

People talk about trusting their “gut instincts” when making a decision. It turns out the gut plays an enormous role not only in our judgments, but also in our overall health and mental well-being.

Over the past 10 years or so, researchers have taken a keen interest in the microbiome—the ecosystem of trillions of bacteria that reside in our gastrointestinal tracts. This complex community of tiny organisms, which scientists refer to as the gut microbiome or gut flora, influences our metabolism, immune system, and cognitive functioning.

Think of your microbiome as an orchestra: An ensemble made up of many members playing different instruments, but they work collectively and harmoniously. When your microbiome is well-balanced, “good” bugs keep “bad” bugs in check and together, they extract energy from food, defend our internal systems from foreign invaders, and keep our body humming.

If the microbiome gets out of tune, the result may be gastrointestinal distress and food sensitivities at the very least. Now, researchers believe that disturbances in gut flora are also linked to a variety of medical conditions—including obesity, diabetes, metabolic syndrome, cardiovascular disease, and autoimmune disorders—by creating conditions in the body that allow these conditions to flourish.

The health of our gut flora also intersects with stress, anxiety and depression in interesting ways. Disharmony in the microbiota appears to influence mood, and vice versa, via what scientists call the gut-brain axis. In mice studies, scientists have found that intestinal microbes maintain the health of the central nervous system and cognitive function as well as regulating stress response, social behavior, and anxiety.

Although the relationship is not well understood yet, it may explain the common occurrence of digestive complaints in people who are stressed depressed—and conversely, the high rates of depression among people with irritable bowel syndrome and other digestive maladies.

The same holds true of many autoimmune disorders, which typically have both physical and psychological symptoms such as fatigue, muscle aches and joint pain, and difficulty concentrating. Evidence suggests that the gut microbiome may play a role.

For example, a study published last year found that gut flora looked different in people with Hashimoto’s thyroiditis as compared to healthy individuals. Although the general mix of bacteria was similar, levels of some were higher and others were lower.

Kim of Illinois, lives with Hashimoto’s thyroiditis. She also has a sensitive stomach. She finds that following a mostly Paleo diet—emphasis on meat and veggies, grain products kept to a minimum—helps keep her finicky gut in line and her autoimmune symptoms at bay.

When her autoimmune disorder flares, however, brain fog and fatigue make it harder for her to mind her diet. The unpredictability of her condition ratchet up her stress levels, creating a vicious cycle where her health suffers. “It’s all kind of in bed together,” says the 42-year-old.

For all that science is discovering about the gut-brain axis, researchers say that it’s just the tip of the iceberg. More research is needed, such as studies in human subjects and clinical trails, before the findings progress to evidence-based medical treatments.

The Connection Between Your Gut, Stress and Mental Health

On the two-way highway between brain and intestines, our mental health can also affect the health of our resident microbe community.

“We know that acute and chronic stress can change the composition of the gut microbiota and some data suggests that stress can change the behavior and functional properties of bacteria,” says gastroenterologist Premysl Bercik, MD, associate professor of medicine at McMaster University in Hamilton, Ontario.

Chronic stress also increases the permeability of the gut lining and blood-brain barrier, allowing molecules that normally wouldn’t get into the bloodstream and brain to pass through. Those signals can trigger changes in mood and anxiety-like behavior, says Bercik.

Take Jessica from Cary, North Carolina, for example. When she started experiencing deep fatigue and a constellation of other health issues, a holistic wellness practitioner suggested that “leaky gut” was the culprit, an unconfirmed medical diagnosis that refers to a loosening of junctions in the intestinal lining, allowing more toxins and bacteria to escape into the bloodstream. One result: kicking off inflammation and autoimmune responses.

Jessica, a marathon runner, initially thought she was burnt out from her intensive training. But she started breaking out in rashes and her stomach rebelled, reacting badly to her regular diet.

When she started to experience anxiety and “horrible sadness,” which weren’t normal for her, Jessica knew something was going on beyond too many miles.

She started taking probiotic supplements, eating a nutrient-rich diet and running less. And it’s helped. At first, she couldn’t tolerate foods like yogurt but now can.

“My physical, mental and emotional health have all not only been restored, but strengthened,” she says. “My diet is more balanced and I am able to tolerate things I couldn’t before … without being spun into a depression or having swollen joints.”

Stress was the tipping point for Jesse. Last year, the 34-year old from Vancouver, Canada started experiencing debilitating insomnia after a demanding period at work. When his doctors couldn’t pinpoint the root cause of his sleep trouble (he lives a healthy lifestyle), he consulted a naturopath who said an overgrowth of Candida, a type of yeast, was thriving off his stress and responsible for his sleep problems.

“My gut was so active at night, essentially feeding signals to my brain and keeping it active and making it difficult for me to fall asleep,” he says.

Jesse began to eliminate certain foods from his diet—sugar, carbohydrates, dairy, and caffeine among them—and noticed immediate benefits.

According to the Anxiety and Depression Association of America, more than half of IBS sufferers have anxiety and/or depression. “When patients with IBS have a flare, it’s also accompanied by worsening psychiatric symptoms,” says Bercik.

What About Probiotics?

Probiotics have attracted a lot of buzz recently. Proponents claim they help with everything from obesity and irritable bowel syndrome to allergies to anxiety and depression by rebalancing your microbiome with healthy bacteria found naturally in food like yogurt, pickles, and tempeh or in supplements.

But experts say probiotics are still a work in progress and more research is needed. Many studies on probiotics have been conducted in animals, says Bercik. Studies in humans show that probiotics can help in a handful of specific circumstances ulcerative colitis or diarrhea caused by C. difficile, “bad” bacteria that can colonize the intestines when antibiotics disturb the normal balance.

Plus, many products on the market, like probiotic-enhanced beverages and supplements, may not live up to their hype, Bercik says. And probiotic supplements aren’t regulated by the Food and Drug Administration, which means supplement makers don’t have to prove the pills’ effectiveness.

“Manufacturing qualities and standards aren’t the same for all products. Sometimes what’s written on the label isn’t what’s found in the pill itself and the bacteria may not be viable,” says Bercik. “It’s a minimally regulated area of the market.”

To that point, a 2015 study of 16 different probiotic products found that only one contained the bacterial strain listed on the label.

Feed Your Gut

If you want to improve your gut health, researchers say that your best bet is to focus on eating a well-balanced, varied diet.

“There’s enormous evidence that shows that traditional diets, like Mediterranean-style or Asian diets that are predominantly plant-based, and where protein comes main from fish, are best for your microbes and health,” says Emeran Mayer, MD, PhD, author of The Mind-Gut Connection and a longtime researcher into neurobiology and the digestive system.

In fact, Australian researchers found that a nutritious diet improved depressive symptoms among participants.

For Amber, changing her diet was key to solving her gut issues, which were exacerbated by her stressful job.

“Every day I would go to work with bloating in my lower belly.” says the Denver, Colorado resident, now 34.

She started to become sensitive to dairy and soy in her diet too.

“I would have bloating like I was five months pregnant,” she says. Her binge eating habits led to sugar cravings and more bloating. “I recognized that something was wrong with my gut and that I needed to mend it.”

Amber started paying closer attention to the foods she ate and discovered that she had an overgrowth of candida, too. She began removing inflammatory foods, sticking with the GAPS Diet (Gut and Psychology Syndrome) and taking probiotics. By removing foods that are difficult to digest and damage the gut flora the Diet allowed her gut to heal. Her digestion improved and her bloating ceased.

The Bottom Line

While researchers are excited about the possibilities of the microbiome and gut-brain axis, they emphasize that they are just scratching the surface.

“I do think that gut bacteria plays an important role in many disorders but we have to be cautious because many diseases will lead to changes in the microbiota. We have to be careful when we talk about what is the cause and what is the consequence and be careful not to jump to conclusions,” says Bercik.

“If it’s all shown to be true, it will open new avenues to treat patients not only with GI or metabolism disorders but also mood and psychiatric disorders.”

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THE GUT-BRAIN AXIS

The gut-brain axis is more a concept that a physical construct that some scan or X-ray could detect. The phrase is used to describe the constant flurry of communication between the two organs.

How fast and furious the communication depends on two barriers: the gut and the blood-brain barrier. These gatekeepers decide what molecules enter or exit the organs in question.

“Both are flexible and can increase or decrease permeability. They determine how much of the signal gets through,” says Emeran Mayer, MD, PhD, author of The Mind-Gut Connection.

Feeling nausea when you’re anxious before a performance, stomach pains when you’re depressed, or “butterflies” when you’re excited all reflect the curious connection between emotions generated up-top in the brain and sensations down below. We’re definitely talking two-way radio here—and it appears the gut may be bossier than the brain.

Mayer, who is on the faculties of medicine, physiology, and psychiatry at the David Geffen School of Medicine at UCLA, explains that microbes in the gut influence intestinal production of hormones such as dopamine and serotonin and neurotransmitters such as GABA—chemical messengers which are known to affect mood, memory, energy levels, and sleep.

In fact, “peripheral serotonin” made in the gut accounts for an estimated 90 percent of total serotonin in the body.

Meanwhile, some hundred million neurons lie embedded in the walls of your gut, constituting the enteric nervous system. This network is sometimes called a “second brain” because it operates pretty much independently, directing the chemical processes and muscle contractions that make digesting and eliminating our food happen.

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GLOSSARY

Bacteria: Microscopic single-celled organisms lacking a distinct nucleus are known as bacteria. Though some bacteria can cause food poisoning and infectious diseases in humans, most are harmless and many are beneficial.

Microbe: Microbes, or microorganisms, include bacteria, protozoa, fungi, algae and amoebas. Many people think of microbes as simply the causes of disease, but every human is actually the host to billions of microbes, and most of them are essential to our life.

Microbiome/microbiota: the full genetic complement of bacteria and other organisms at home on your skin, gums, and teeth and especially in your intestinal tract.

Probiotic: These good-for-you bacteria are found naturally in food like yogurt with live cultures, sauerkraut, and kimchi (generally fermented or pickled), in supplements, and in snacks and beverages enhanced with probiotics.

Psychobiotic: Originally defined by researchers as a probiotic with a positive impact upon mental health, the term has been broadened to encompass any strategy that can modify mental health via the microbiota.

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CHOOSING A PROBIOTIC

If you’re interested in trying a probiotic supplement, the American Gastroenterological Association offers this advice:

Talk to your doctor: Some probiotics may interact with other medication that you’re currently taking. Your doctor may also have recommendations for specific supplements to try and what to look for.

Read the label: Which groups, species and strains of bacteria are in the probiotic? How many microbes does it contain? What’s the use-by date? Pro tip: More bacteria doesn’t necessarily mean that it’s a better choice.

Check the fit: If you’re taking the probiotic for a specific condition, has the supplement’s specific group, species, and strain of bacteria been proven beneficial in scientific research?

Start with established companies: Larger companies will likely have better quality control and manufacturing standards. They may also be more likely to have tested their products in clinical research.

1 COMMENT

Ocean1

This “new” connection seems overdue for mainstream scientific documentation as these concepts have long been the basis of naturopathic, homeopathic and “health food” healing practice. Thank you for publishing detailed and balanced article here.
Of course the first course of action stated herein is to “consult
your doctor”. Many MDs who have been trained in allopathic medicine have been deprived of training in homeopathy or naturopathic medicine. This means a patient may often receive a caveat from their MD about “unproven” ways of healing. As methods become “proven” pharma based medicine will properly make way for nutritional advice and healing. At the moment a traditionally trained MD may smile a patronizing smile and dismiss the question as “let me know how it works out”? Or an open minded MD may be criticized for stepping beyond the realm of verifiable treatment and risk their relationship with their certifying board or their peers. More information published this way empowers readers to find particular empirical methods that may successfully permit the individual to “own” our own health outcomes. Thank you.

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HEALTHY HABITS

Most of us don’t default to healthy habits. It takes planning and effort, and sometimes a surge of self-discipline, to eat right, exercise, get the sleep we need, and stay on top of work and life tasks. Establishing new habits, let alone purging bad ones, can require major effort, especially if we are also struggling with depression or anxiety. What are some good habits that you've formed and how did you build them?